The present embodiments relate to dynamic CT imaging.
Modern imaging methods are frequently used to generate two-dimensional or three-dimensional image data that may be used to visualize an imaged examination object and additionally for further applications.
The imaging methods are frequently based on the detection of x-ray radiation, with projection measurement data being generated. Projection measurement data may be acquired, for example, with the aid of a computed tomography system (CT system). With CT systems, a combination of x-ray source and opposing x-ray detector arranged on a gantry travels around a measurement space, in which the examination object (e.g., the patient) is located. The rotation center (e.g., the isocenter) corresponds, for example, to a system axis z. During the course of one or more circuits, the patient is irradiated with x-ray radiation from the x-ray source, with projection measurement data or x-ray projection data being captured with the aid of the opposing x-ray detector.
The generated projection measurement data (e.g., projection data) is a function, for example, of the model of x-ray detector. X-ray detectors may have a plurality of detection units (e.g., arranged in the form of a regular pixel array). The detection units each generate a detection signal for x-ray radiation striking the detection units. The detection signal is analyzed at defined time points with respect to intensity and spectral distribution of the x-ray radiation in order to provide information about the examination object and generate projection measurement data.
Reconstructed three-dimensional CT volumes are routinely used when planning radiation therapy for patients with lung and abdominal carcinomas. In order to be able to reconstruct the anatomy of a patient in a defined phase, a respiratory surrogate is used in synchronicity with the raw data acquisition in order to be able to establish a correlation between raw data and patient respiration. There are different options for radiation planning. A number of phases covering the entire respiratory cycle may be reconstructed. Such a reconstruction is also referred to as four-dimensional CT imaging. This is used to localize the movement of tumors and tissue at risk over the respiratory cycle to keep the planning target volume PTV as small as possible, thereby reducing the radiation exposure of the patient to be treated as far as possible. The accuracy of such planning is a function of the image quality of the 4D CT reconstructions. These are, however, very frequently impaired by 4D artifacts, as the external respiratory surrogate only reproduces the internal anatomy to a limited degree.